If you've ever seen your accuracy go down the drain and your screen get blurry in the middle of a firefight for no apparent reason.

That is suppression. It is very effective when utilized.

Suppression is a tactic in which a soldier (usually someone with some type of Machine Gun) opens fire on an enemy or group of enemies, not with the intent to kill them, but with the intent to reduce their combat effectiveness through fear of death.

The Space Marine Devastator can equip a Heavy Bolter, a firearm designed to unload a large amount of powerful munitions into an area accurately. (The Chaos Marines have the Heavy Bolter as well)

The effects of being suppressed are

• Decreased accuracy (to an essentially useless point)
  
• Blurred vision
  
• A suppression marker (two arrows pointing down at you) (can also be interpreted as a debuff marker)

The suppression marker can be seen by everyone. It is effective as a spotting tool because you don't even have to be able to see the enemy to do it. If they're taking cover behind a low wall, you can shoot over the low wall and the suppression marker will pop up.

If you see an ally with the suppression marker over their head. Know that they cannot effectively defend themselves. Help them.

Suppression does not last forever, but it doesn't go away relatively quickly either.

To suppress an enemy (and also your allies, so be careful) you simply fire a few heavy bolter rounds at them. The shots don't even have to hit them. You just need to shoot at minimum 1-5 shots (I think it's based off the class you're trying to suppress, or how close your shots get) past them within about 2-3 meters. It doesn't even matter how many enemies these shots pass, they will suppress ALL OF THEM

At this time you can only suppress enemies with the heavy bolter.

If you see a Devastator braced up on some cover looking over an area that's likely to see a lot of enemies (the towers at the beginning of blackbolt defense station for example), and you want a break from actively running around to defend/attack. Sit by the devastator for a while to provide cover for them. While braced up, the devastator can't even see their own marine. So they likely won't know when an Assault comes up behind them to murder them. I can almost guarentee that after a short while of the Devastator shooting at the enemies, an intuitive enemy will come along to take out the Devastator thinking that he's alone.

The suppression effect starts at 100%

You can continue shooting at suppressed enemies to keep the suppression effect at 100%.

You don't even need to be braced up on some cover. You can just hip fire into some enemies to suppress them due to the fact that it doesn't require pinpoint accuracy. HOWEVER, if you are not braced on some cover, landing consecutive shots to take down approaching enemies can be difficult.

Suppression is effective on both defense AND offense.

You will get 50xp for any enemy killed while affected by your suppression.

If you are running around and you see a devastator locking down an area with suppression. If you have ammo packs equipped, give them one, you have 2, and I can almost guarantee that you will die before you need the second or get to an ammo crate. This will refill the devastator's heavy bolter ammo all the way back up to 500, and will increase the time they have untill they have to back into cover to resupply themselves.

And if you see a Devastator locking down an area with suppression and they ASK for ammo with the voice commands. Give them an ammo pack. It's a pretty safe bet that, at that point, they know what they're doing.

HEAVY BOLTER SCARY
SHOOT AT ENEMY
ENEMY HIDE
ENEMY UNHIDE
SHOOT AT ENEMY AGAIN
WATCH AS GLORY OF THE EMPEROR WASHES OVER ENEMY, RENDERING THEM USELESS